In recent years, with the increase in communication channel capacity and communication distances, there have been developments to increase the capacity of and the distance covered by networks. For backbone networks, in order to implement an increase in the capacity of and the distance covered by networks, studies have been conducted on an optical network (hereinafter, referred to as a “WDM network”) that uses wavelength division multiplex (WDM). The WDM network uses an optical transmission device, which is called a reconfigurable optical add/drop multiplexer (ROADM), that adds an arbitrary wavelength to wavelength multiplexed light, which is targeted for transmission, and drops an arbitrary wavelength from the wavelength multiplexed light.
The reconfigurable optical add/drop multiplexer includes a monitor, such as an optical channel monitor (OCM) or the like, that detects the value of the optical power of each wavelength in the wavelength multiplexed light that is targeted for transmission. Furthermore, the reconfigurable optical add/drop multiplexer includes a control mechanism that controls the adjustment level of the optical device such that the value of optical power of each wavelength matches the target value on the basis of the detection result obtained by the monitor. The control mechanism is implemented by, for example, firmware.
Consequently, in the reconfigurable optical add/drop multiplexer, if the control mechanism is rebooted when the firmware is updated, the control performed by the optical device that adjusts optical power of each wavelength is stopped, which may possibly make communication unstable.
In contrast, there is a known technology in which a control mechanism backs up the adjustment level, which was set in the optical device before the control performed by the optical device is stopped, in a storing unit as a fixed value and then continuously sets the adjustment level, which has been backed up as the fixed value, in the optical device in which the control has been stopped.
Patent Document 1: Japanese Laid-open Patent Publication No. 2009-253426
Patent Document 2: Japanese Laid-open Patent Publication No. 2009-117970
However, in the conventional technology, there is a problem in that it is difficult to maintain the stability of communication when control performed by an optical device is stopped.
Specifically, in the conventional technology, because the adjustment level, which is a fixed value, is continuously set in the optical device in which a control is stopped, if the optical power of each wavelength in wavelength multiplexed light varies during the stopping of control that is performed by the optical device, it is difficult to maintain the value of optical power of each wavelength at its target value after the optical power of the wavelength has been changed. Consequently, with the conventional technology, there is a problem in that stability of communication may possibly be prevented from being maintained during the stopping of control that is performed by the optical device.